Method of increasing volumetric throughput of an internal combustion engines used in vapor destruction applications

ABSTRACT

A method and device for controlling emissions of VOC&#39;s comprises transporting VOC&#39;s to an engine and transporting the exhaust from the engine into a manifold. Supplemental air is transporting into the manifold and heat is transferred from the exhaust to the supplemental air within the manifold. The supplemental air is mixed with the exhaust and the mixture is transferred to a pollution abatement device.

PRIORITY

The present application claims the benefit of U.S. ProvisionalApplication No. 61/467,242, filed Mar. 24, 2011, the disclosure of whichis hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Field

The embodiments disclosed herein relate to a system and method forcontrolling emission of Volatile Organic Compounds and, morespecifically, to an improved system and method for increasing volumetricthroughput through an internal combustion engine used to controlVolatile Organic Compounds.

2. Description of the Related Art

The direct release of Volatile Organic Compounds (VOC's) into theatmosphere has been for some time now recognized as a primarycontributing factor in affecting ozone concentrations in the loweratmosphere. The EPA has established standards for safe levels of ozone,and local air quality districts have implemented regulations andmandated control measures pertaining to the release of hydrocarbonvapors into the atmosphere, from operations such as soil remediation,storage tank inerting, and storage vessel loading and unloading; thathave been identified as sources of hydrocarbon emissions responsible forimpacting ozone levels.

The process of treating these vapors, through any of a variety ofmethods, is typically referred to as “degassing”; which is either thecollection or on-site destruction of these vapors as an environmentallyresponsible alternative to their otherwise direct release into theatmosphere.

The internal combustion engine, as well as open-flare incinerator units,have been employed for several decades as a means of on-site destructionof these VOC's by elemental combustion. The combustion process doesitself give rise to the undesirable production of carbon monoxide andnitrogen oxides; however this has been accepted as a reasonableconsequence for the nearly 99% efficiency in the destruction ofhydrocarbon based VOCs. These consequential emissions are accepted, buttolerated only to a regulated extent, and are also a factor to beconsidered in engines and incinerators employed in vapor destructionapplications. The maximum permissible limits of consequentialhydrocarbon, carbon monoxide and nitrogen oxide emissions are regulatedto different standards within different air quality regions.

The many different VOC's typically subject to treatment represent a widerange of hydrocarbons between C1 through C10 along with theircorresponding alcohols and ketones. Each of these individual compoundsis characterized by having unique upper and lower flammability limits,expressed as a range of concentration in atmospheric air within which asource of ignition results in combustion of the mixture. This data iswell established and widely published; along with the stoichiometricmixture ratio for each of these compounds, defined as the theoreticallyideal mixture at which combustion will be complete without a remainingexcess of either air or fuel. Generally, combustion is most completewith a slight excess of air, approximately 15%, being slightly leanerthan the theoretical stoichiometric mixture concentration.

The internal combustion engine, as well as open-flare incinerator units,have been employed for several decades as a means of on-site destructionof these Volatile Organic Compounds by elemental combustion; but eachwith slightly different performance characteristics. In the case of theopen-flare incinerator unit; the VOCs to be processed are typicallyintroduced at a vapor concentration equivalent to or less than the lowerexplosion limit and passed over a continuously maintained flame sourceresponsible for combustion of the subject VOCs. Open-flare incineratorunits are able to support combustion of the introduced VOCs atconcentrations less than the lower explosion limit by virtue that theflame front has already been established by a continuously maintainedpilot flame. The disadvantage of the open-flare incinerator unit is thatthe inlet concentration is limited by the ability of the unit todissipate the amount of heat generated by the combustion of VOCs, basedupon the heat content of the VOCs undergoing treatment. A furtherdisadvantage of open-flare incinerator type units is that greenhousegasses (CO2) are continuously generated by the pilot flame withoutrelation to the mass quantity of VOCs being processed.

In the case of the internal combustion engine employed in vapordestruction applications, the resultant heat produced from combustion ofthe VOCs is very effectively handled by the engine cooling system,affording VOC concentrations in the upper range approaching the upperexplosion limit. The internal combustion engine is also self-sustainingin that the fuel source is entirely that of the subject VOC itself anddoes not require any addition of fossil fuel until the concentration ofsubject VOC falls below the lower explosion limit of the subject VOCundergoing treatment.

It is important to note that the aforementioned values of lower andupper explosion limits as defined for subject VOC's undergoing treatmentwas established in a laboratory setting and under the thermodynamicprinciples of a constant pressure (Cp) type process. Actual conditionsof combustion within the internal combustion engine, whether sparkignited or compression ignited, more closely resemble combustioncharacteristic of a “constant volume” (Cv) type process and typicallymust therefore be adjusted. This adjustment is on the order ofapproximately 15% above the lower explosion limit (herein defined as thelean limit), and approximately 15% below the upper explosion limit(herein defined as the rich limit).

Because the many VOCs typically subject to treatment are too numerous toelaborate herein, gasoline vapor has been selected as the model forpurposes of discussion. In selecting gasoline vapor; it is hereindefined as having an upper explosion limit of 7.5%/vol; with a lowerexplosion limit of 1.5%/vol; and a stoichiometric value of 4.5%/vol.Adjusting these values for practical combustion ranges within theinternal combustion engine operating under the thermodynamic principalsof a constant volume combustion process; the rich limit is defined as6.5%, the lean limit as 2%, and the stoichiometric ratio as 4.5%. Thereare many factors which could influence these specific values; but thesevalues are selected for the purpose of discussion herein.

The internal combustion engine employed in vapor destructionapplications has traditionally been that of the “lean-burn” type;wherein the process vapor is introduced at a concentration value lessthan stoichiometric and more closely approximating that of thelean-limit for the subject VOC. At this lean mixture, the resultantemissions with regard to hydrocarbons and carbon monoxide, tend to be attheir lowest value, and remain low up to the lean-limit where aftercombustion is no longer possible. Oxides of nitrogen emissions tend toincrease dramatically on the immediate lean side of stoichiometric, butthen fall in value as the mixture becomes increasingly lean up to thelean limit. These engines are typically fitted with“reduction/oxidation” type catalytic convertors as a final polish to theexhaust stream prior to emitting into the atmosphere.

Although lean-burn operation is a sought after objective for modernengines employed in power producing applications, such as motor vehicleand industrial power applications wherein fuel efficiency and minimalexhaust emissions are of primary concern; this is not the idealconfiguration for such engines employed in vapor destructionapplications wherein maximum fuel consumption in terms of vaporprocessing volumetric throughput are of primary interest.

SUMMARY

A lean-burn engine employed in processing gasoline vapor equates to avapor processing rate of 2% of the total volumetric throughput of theengine. In the case of the engine with a total displacement volume of500 cfm, this equates to a VOC processed volume of: [500(0.02)], or 10cfm. The same engine operating in rich-burn mode, processing vapor at 6%by volume equates to a VOC processed volume of: [500(0.06)], or 30 cfm.This is a 3-fold increase being a linear function of the proportionateincrease in vapor concentration up to the rich-limit, where aftercombustion is no longer possible.

Although the internal combustion engine has the inherent ability to copewith and dissipate the heat energy associated with combustion of VOCs atthe upper extreme of their rich-limit, it is important to note thathydrocarbon and carbon monoxide emissions increase substantially whenoperating on the rich side of stoichiometric, along with a correspondingdecrease in excess air within the final exhaust stream. Because mostengines employed in vapor destruction applications are equipped with acatalytic convertor, requiring a certain excess of atmospheric air aspart of the exhaust stream for proper catalytic convertor function,these engines must typically operate on the lean side of stoichiometricas a necessity for catalytic convertor function.

The internal combustion engine, as part of prior art employed in vapordestruction applications, has been limited in realizing its fullpotential in terms of volumetric throughput of processed vapors; due tothe natural increase in hydrocarbon and carbon monoxide emissionsassociated with rich-burn operation, and also that of requiring anexcess of air in the final exhaust stream essential to support propercatalytic convertor operation.

Accordingly, one embodiment comprises a system for controlling emissionsof VOC's by combustion of said VOC's in an internal combustion engine.The system can include an inlet conduit for connection to a source ofVOC's, an internal combustion engine that is connected to the inletconduit; exhaust path that receives exhaust from the internal combustionengine and an air source of supplemental air. A manifold comprises afirst conduit that receives the exhaust from the exhaust path and asecond conduit that receives supplemental air from the air source. Themanifold is configured to transfer heat from the exhaust in the firstconduit to the supplemental air in the second conduit. An abatementdevice is in fluid communication with the first conduit downstream ofthe manifold. A fourth conduit is in communication with the firstconduit upstream of the abatement device.

In another embodiment, a method of controlling emissions of VOC'scomprises transporting VOC's to an engine and transporting exhaust fromthe engine into a manifold. Supplemental air is transported into themanifold and heat is transferred from the exhaust to the supplementalair within the manifold. The supplemental air is mixed with the exhaustand at least a portion of the supplemental air and exhaust mixture istransported into a pollution abatement device.

Other embodiments and arrangements are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration a degassing system according to oneembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described herein, one embodiment can include a method of employingsecondary “thermal oxidation” for increased volumetric throughput andreduced hydrocarbon and carbon monoxide emissions from internalcombustion engines employed in “degassing” operations. As describedherein, “degassing” operations is intended to be a broad term that canbe generally defined as the destruction of Volatile Organic Compounds,by elemental combustion, of hydrocarbon vapors emanating from soilremediation, in situ process streams, pipelines and storage vessels; asan environmentally responsible alternative to the otherwise directrelease of these vapors into the atmosphere. In other embodiments, thedegassing operations can also be applied to other compounds and/or fromsources other than those listed above.

One advantage of certain embodiments is that an internal combustionengine, as employed in certain embodiments, can operate at richer thanstoichiometric mixtures for greater vapor processing capability withoutconsequential increase in the production of hydrocarbon and carbonmonoxide emissions typically associated with rich-burn engines; andwhile also reducing oxides of nitrogen emissions inherent to internalcombustion engines capable of operating on the rich side ofstoichiometric air/fuel ratios.

One advantage of the certain embodiments is that they allows theinternal combustion engine as typically employed in vapor destructionapplications to operate at the upper range of the flammability limit forthe VOC being processed, without the corresponding increase inhydrocarbon and carbon monoxide emissions normally associated withoperation in this upper range, and provides a method to an exhauststream containing sufficient excess air to support proper catalyticconvertor operation.

Certain embodiments allow the internal combustion engine to operate atgreater than stoichiometric mixture ratios for the particular VOC beingprocessed, by providing an intermediate stage of combustion immediatelyfollowing combustion within the engine, that allows combustion toproceed under lean-burn constant-pressure conditions in an environmentof excess air that not only supports more complete combustion but alsoprovides sufficient excess air in the final exhaust stream essential tosupport proper catalytic convertor operation.

In one arrangement, the exhaust stream immediately following exhaustfrom combustion within the engine can be passed (e.g., via a conduit)into a heated manifold wherein air is injected (e.g., via a conduit)from an outside source such to effectively reduce the relativeconcentration and assimilate combustion under lean-burn andconstant-pressure conditions with sufficient excess air necessary tosupport subsequent introduction to the catalytic convertor for a finalpolish before finally being emitted to the atmosphere.

In such arrangements, a several-fold increase in the volumetricthroughput of processed vapors within the fixed displacement of theengine itself, without increase in exhaust emissions typicallyassociated with operation in rich-burn mode, and provides alsosufficient excess air in the final exhaust stream necessary to supportproper catalytic convertor operation.

FIG. 1 is a schematic illustration of one embodiment of a degassingsystem. In the illustrated embodiment, the subject VOC is introducedinto the system at point (1). In the case of soil remediation or in situprocess streams (for example), the vapor concentration at point (1) mayremain very constant or substantially constant at some value rangingbetween 0% to 100%/volume over an indefinite period of time. In the caseof processing a fixed volume of VOC vapors, such as from storagevessels, the concentration at point (1) can commence at a value of100%/volume concentration and can eventually fall to 0%/volume at theconclusion of the “degassing” event. Accordingly, the VOC concentrationmeasured at point (1) can be a variable that may change over time.

In the illustrated embodiment, when the vapor concentration as measuredat point (1) is substantially equal to or greater than the upperexplosion limit (or some calculated or predetermined reference value),or more accurately the predetermined “rich-limit” for the subject VOC;dilution air can be introduced at point (2) such that the vaporconcentration as measured at point (3) is equal to the predetermined“rich-limit”. When the vapor concentration as measured at point (1)falls below the upper explosion limit, or the predetermined“rich-limit”, dilution air is no longer required. When the vaporconcentration as measured at point (1) falls substantially below thelower explosion limit (or some calculated or predetermined referencevalue), or the predetermined “lean-limit”; a supplemental fuel (such asmethane or propane or other) can be introduced at point (4) such thatthe combustible mixture as measured at point (5) is equal to orsubstantially equal to the “lean-limit” necessary to sustain combustionwithin the engine. When the subject vapor concentration as measured atpoint (1) falls within the range of the “rich” and “lean” limit; neitherdilution air nor supplemental fuel are necessary to form a combustiblemixture. Accordingly, in one embodiment, the VOC vapors being processed,can be introduced at a concentration ranging from 100%/vol to 0%/vol andcombustion is still supported within the engine employed in vapordestruction processes, and can thereby process the subject VOC vapors to0% in vapor destruction “degassing” operations.

An advantage of the internal combustion engine employed in vapordestruction applications is its inherent ability to cope with thecombustion heat generated from operation in the upper range of theflammability limit. In the case of the engine processing gasoline vapor,this equates to a concentration value of approximately 6% versus theapproximate 2% normally associated with engines operating in lean-burnmode of operation.

When the vapors to be processed are introduced into the engine at thelean-limit (e.g. 2% for gasoline); the volumetric throughput for aninternal combustion engine with a displacement volume of 500 cfmbecomes:

[(0.02)500]=10 cfm processed vapors(in lean-burn mode)

When this same engine is operated in rich-burn mode, wherein the vaporsto be processed are introduced at their “rich-limit” (e.g. 6% forgasoline); the volumetric throughput for the same engine with adisplacement volume of 500 cfm becomes:

[(0.06)500]=30 cfm processed vapors(in rich-burn mode)

Although the numbers are only relative, it represents a 3-fold increasein volumetric throughput for the same engine when operated in thisrich-burn mode.

One associated benefit with operation in rich-burn mode, is that oxidesof nitrogen emissions tend to be at their lowest values due to reducedcombustion temperatures and the increased heat capacity of the system.The primary disadvantage however; is that hydrocarbon and carbonmonoxide emissions tend to increase substantially due to the absence ofsufficient excess air to facilitate complete combustion, and the absenceof sufficient excess air in the final exhaust stream essential to propercatalytic convertor operation. A certain excess of nitrogen is essentialto the reduction phase of the catalyst, and a certain excess ofatmospheric oxygen is essential to the oxidation phase of the catalyst.

The embodiments describe herein can allow the engine to operate inrich-burn mode for maximum volumetric throughput of processed vapors,while still providing sufficient excess air in the exhaust stream tofacilitate complete combustion and with sufficient excess air in thefinal exhaust stream necessary for proper catalyst function.

With continued reference to FIG. 1, a conduit transfers the VOC vaporsand any dilution air and/or supplemental fuel to the engine 6. As theengine 6 operates an exhaust stream is generated and transferred to aconduit. Atmospheric air can be introduced into the exhaust stream as itleaves the combustion chamber at point (7) in the conduit before theexhaust stream passes into the thermal oxidizer exhaust manifold (8).The atmospheric air can be supplied by source (10), which can be eitheran exhaust driven turbocharger, roots blower, or other source such as anexternal air compressor. The conventional turbocharger, properlyselected for the application, is herein suggested as a proven andpreferred method due to its compact size but more importantly theability to closely regulate its volumetric output with a minimum ofcomplex controls.

In the illustrated arrangement, the introduced air from source (10) canbe passed through an annular space (11) surrounding the thermal oxidizerexhaust manifold (8) in such a way that the natural heat of the exhaustgas passing through the manifold is transferred to the introduced air.This serves not only to provide cooling to the manifold from the hotexhaust gas passing within, but also imparts this heat to the introducedair stream such to maintain an elevated temperature (e.g., approximately1200 F in one arrangement) at the point wherein this air is injected tothe exhaust stream as it leaves the combustion chamber at point (7). Ifthe introduced air is not maintained at this elevated temperature, thengas phase termination of active specie in the exhaust gas could occur;resulting in excessive hydrocarbon and carbon monoxide emissions. Themanifold may or may not be fitted with insulation (not shown) to aid inretaining the natural heat within the manifold and imparting this heatto the introduced air rather than the surrounding environment. Themixture of exhaust gases and heated supplemental air can then betransferred via a conduit 12 to the catalytic convertor 13.

In order to determine the amount of supplemental air necessary to beintroduced in converting from lean-burn to rich-burn mode of operation;in one embodiment, the vapor concentration associated with operationunder lean mode of operation is determined and the amount of normalengine air based upon the fixed displacement volume of the engine isdetermined.

For example, in the arrangement of the engine with a displacement volumeof 500 cfm, operated in lean-burn mode having a vapor concentration of2%:

engine air=(98%)500=490 cfm

VOC volume=(2%)500=10 cfm

The amount of supplemental air required for conversion to rich-burn (6%concentration) therefore becomes:

[(Crich/Clean)−1](engine air)=supplemental air

-   -   or in this case:

[(0.06/0.02)−1](490)=supplemental air=980 cfm

The amount of excess air now present in the exhaust stream by theaddition of supplemental air is such to return the total mixture to theequivalent of operation in lean-burn mode, as:

30/(490+980)=2%/volume=(original lean-burn conditions)

It is interesting to note also that although the total heat capacity ofthe system within the thermal oxidizer manifold has increased by theaddition of supplemental air, the heat produced within the system hasincreased commensurately; such that exhaust gas temperature remainsrelatively unchanged from that of operation in lean-burn mode. Incertain arrangements, this can be an important factor in maintainingproper catalyst temperature.

The total volume quantity of exhaust gas passing through the catalyst,has now been increased several fold by the introduction of supplementalair; which may have a significant impact upon proper catalyst operation.Not only is there an increased concern for excessive back pressureproduced in the exhaust system, but also an increase in gas density anda corresponding decrease in residence time within the catalyst, thatcould be detrimental to proper catalyst operation. This potentialcondition for the particular catalyst employed can be considerable, andthe addition of a supplemental catalyst in parallel, or an appropriateretrofit can be part of a particular application.

According to certain of the embodiments described above, a method isprovided by which the volumetric vapor processing capability can beincreased by several fold within the internal combustion engine having afixed displacement volume, when the vapor concentration to be processed(as measured at point 1) is greater than the upper explosion limit orthe predetermined rich-limit for the particular VOC undergoingtreatment. Although this can afford a several fold increase in the vaporprocessing capability of the system when the VOC concentration isgreater than the predetermined rich-limit; such embodiments provide noimprovement in the volumetric throughput of the system when the inletconcentration measured at point (1) falls below the lower lean-limit.The continued introduction of supplemental air at this point mayactually be detrimental to the performance of VOC destruction in thatexcessive amounts of supplemental air are not needed and may bedetrimental to the chemistry of proper catalyst operation in addition toreduced exhaust gas temperatures resulting in excessive cooling andreduced performance of the catalyst.

For this reason, it is suggested in certain embodiments, that theintroduction of supplemental air be terminated when the subject VOCconcentration as measured at point (1) falls below the predeterminedlean-limit for the particular VOC undergoing treatment.

As described above, in the illustrated embodiments a reciprocatinginternal combustion engines is used. However, it is contemplated thatother types of engines and/or internal combustion engines could beutilized in modified embodiments.

As used herein the term “conduit” is intended to be a broad term thatincludes, pipes, ducts and channels. In addition, a conduit need not bea separate device or element but can define portions of a longerconduit. That is, a first and second conduit can be portions orsub-sections of a larger conduit.

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. In addition, while a number of variations of the invention havebeen shown and described in detail, other modifications, which arewithin the scope of this invention, will be readily apparent to those ofskill in the art based upon this disclosure. It is also contemplatedthat various combinations or subcombinations of the specific featuresand aspects of the embodiments can be made and still fall within thescope of the invention. Accordingly, it should be understood thatvarious features and aspects of the disclosed embodiments can becombined with or substituted for one another in order to form varyingmodes of the disclosed invention. Thus, it is intended that the scope ofthe present invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims.

1. A system for controlling emissions of VOC's by combustion of saidVOC's in an internal combustion engine, the system comprising: An inletconduit for connection to a source of VOC's, an internal combustionengine that is connected to the inlet conduit; an exhaust path thatreceives exhaust from the internal combustion engine; an air source ofsupplemental air; a manifold comprising a first conduit that receivesthe exhaust from the exhaust path and a second conduit that receivessupplemental air from the air source, the manifold configured totransfer heat from the exhaust in the first conduit to the supplementalair in the second conduit; and an abatement device in fluidcommunication with the first conduit downstream of the manifold; and afourth conduit in communication with the first conduit upstream of theabatement device.
 2. The system of claim 1, further comprising a sourceof dilution air connected to the first conduit upstream of the engine.3. The system of claim 2, further comprising a source of supplementalfuel connected first conduit upstream of the engine.
 4. The system ofclaim 3, further comprising a VOC measurement device configured tomeasure the amount of VOCs in the first conduit.
 5. The system of claim4, further comprising a control system operatively connected to the VOCmeasurement device, the source dilution air and the source of supplementfuel and wherein the control system is configured to adjust and amountof dilution air or supplemental fuel in response to the measured amountof VOC.
 6. The system of claim 1, wherein the manifold is configuredsuch that flow through the second conduit and the third conduit are inopposite directions.
 7. The system of claim 1, wherein the abatementdevice is a catalytic convertor.
 8. The system of claim 1, wherein theair source of supplemental air is a supercharger.
 9. The system of claim1, wherein the fourth conduit in communication with the first conduitupstream of the manifold.
 10. A method of controlling emissions ofVOC's, the method comprising: transporting VOC's to an engine,transporting exhaust from the engine into a manifold; transportingsupplemental air into the manifold; transferring heat from the exhaustto the supplemental air within the manifold; mixing the supplemental airwith the exhaust; and transporting at least a portion of thesupplemental air and exhaust mixture into a pollution abatement device.11. The method of claim 10, comprising adding dilution air upstream ofthe engine.
 12. The method of claim 11, comprising adding supplementalfuel to the engine.
 13. The method of claim 12, further comprisingmeasuring VOC concentrations.
 14. The method of claim 13, comprisingadjusting an amount of dilution air and/or supplemental fuel in responseto the measured VOC concentrations.
 15. The method of claim 10, whereinthe supplemental air and the exhaust flow in opposite directions throughthe manifold.
 16. The method of claim 10, wherein the abatement deviceis a catalytic convertor.
 17. The method of claim 10, comprisingpressurizing the supplemental air.
 18. The method of claim 10,comprising mixing the exhaust and the supplemental air upstream of themanifold.
 19. The method of claim 10, wherein the engine is an internalcombustion engine.